Spiritual Forum

The "Size" of the Universe

The distance between the earth and the most distant objects we can "see" is estimated to be about 14 billion light years. That's the distance light—which travels at 186,000 miles in a second—would travel in a full year at that rate, multiplied by 14 billion! But wait. The most distant objects are moving away from us. So after 14 billion years, we are really seeing them as and where they were 14 billion years ago. Today, they are much farther away. So, what is the diameter of the universe today?

Well we can extrapolate from what we know about where they were, the speed at which they were moving away, the amount of time that has passed, and the overall expansion of the universe. What we come up with is an estimated actual distance of 78 billion light years for the most distant objects (that appear to be 14 billion light years away today) and a current diameter estimate for the universe of 156 billion light years.

"But wait!" you cry. "How can that be? We are told that the Church was wrong; the earth is NOT at the center of the universe. So why should we double the distance to the most distant objects to get the diameter, as if we are at the center?"

Ah, silly you. You must have forgotten to take into consideration the implications of our incomprehensible relativity theories, which tell us that ANY point can be taken as the center of the universe. Using sentences like the preceding one (that make fundamentally unintelligible but superficially simple claims) and simple analogies, we can pretend we actually have some understanding of relativity. For examples, consider the balloon and raisin bread universe analogies.

In the balloon analogy, the galaxies are like dots on the surface of a balloon that are all moving away from one another at equal speed as the balloon is blown up. It doesn't matter what spot you select on the balloon; all the other dots around it are moving away from it at the same rate of speed as from any other spot. And then there is the Raisin Bread Universe in which the galaxies are the raisins in the dough (space). As the bread is allowed to rise, all the raisins move away from the other nearby raisins at the same speed. The doughniverse is expanding; using these analogies, for a moment we can pretend that we can truly visualize (understand) the implications of relativity. But the analogies fundamentally break down.

For example, "Wait!" you cry again. "How can that be? We are told that nothing can travel faster than the speed of light. How can we be 78 billion light years away from objects that were 14 billion light years away from where we are now 14 billion years ago? Even at the speed of light, they could only be 14 billion light years further away today, or a maximum of 28 billion light years."

Relativity to the rescue again. You see, the distant galaxies are not only moving away from us through space, space itself is expanding. So the apparent change in distance is a product of the speed of the two objects' motion through space PLUS the expansion of space itself, what has been called the comoving distance. There. No violation of relativity. The distant objects are moving at speeds considerably slower than the speed of light. It is only with the additional effect of space expansion that they appear to be moving faster than light.

All this would be well and good if it made any sense; that is, if it didn't produce more paradoxes than the questions it answers. But consider this: We only have one way of understanding "speed." Speed is the change in distance between two objects over a certain period of time. What is the difference then between two objects moving away from each other through space PLUS the expansion of space itself—which can also only be known by the change in the distance between objects—vs the speed at which a distant object is moving away from us?

Space has no fixed coordinates. So, what does "moving through space" mean without reference to motion relative to other objects in space? Remember that relativity theory tells us that motion can only be detected (be defined by, have any referential meaning, etc.) in relation to other objects. So, if the distance between two objects is increasing faster than the speed of light, isn't one moving away from the other faster than light? If not, what do we mean by "moving?" This is partly why some people consider the comoving distance to be a merely theoretical concept with no physical meaning. Yet, without the comoving distance, many theorists think the Big Bang model collapses.

And to complicate matters further, how can we measure the diameter of something that is infinite and of unknown shape? Space, we are told, has no end and "curves back on itself." As on the surface of our expanding balloon, if you go in a straight line, you will eventually return to where you began. And the distribution of galaxies in the universe may be roughly sphere shaped, like a balloon. So far, the balloon analogy is holding up, if you agree to stay on the surface of the balloon. But what if you were to travel through the center of the sphere directly to the most distant objects on the other side? If you kept going, what would be the shape of the ballooniverse that would bring you back to where you began?

Go know.

http://www.yoism.org/?q=node/319